As a recording/reproducing system of a disc-shaped recording medium, there is an improved constant angular velocity (hereinbelow, referred to as MCAV (Modified Constant Angular Velocity)) system. It is a system which satisfies both of a constant angular velocity (CAV: Constant Angular Velocity) system which attaches importance to high-speed accessing performance in that a rotational speed of a disc is controlled so as to be constant and the nearer a track approaches an outer rim where a linear velocity increases, the higher transfer rates of recording and reproduction are set and a constant linear velocity (CLV: Constant Liner Velocity) system which attaches importance to satisfying both of a predetermined transfer rate of the recording and the reproduction and a high-recording density.
A reproducing apparatus and a reproducing method of a disc-shaped recording medium having zones of different transfer rates as in the MCAV system or the like have been disclosed in the specification of Japanese Patent No. 3106750.
However, the following problems exist in the reproduction of the disc-shaped recording medium of the MCAV system. To allow a head to trace the disc-shaped recording medium and read a reproduction signal, a waveform equalizing circuit for correcting characteristics of the reproduction signal, a clock reproducing circuit to obtain bit synchronization, for example, a PLL (Phase Locked Loop) or the like are necessary. However, the disc-shaped recording medium of the MCAV system has a plurality of zones of the different transfer rates and there is a case where a difference between the transfer rate of the innermost rim and that of the outermost rim reaches three times or more. Therefore, it is very difficult to reproduce the disc-shaped recording medium of the MCAV system by the single clock reproducing circuit.
In the reproducing apparatus having a plurality of heads for reproducing the disc-shaped recording medium of the MCAV system, it is necessary to equip a clock extracting circuit corresponding to the different transfer rates which are used when the respective heads reproduce. In the conventional reproducing apparatus, therefore, there is such a problem that if signal processes of transfer rates in a wide range are enabled, parts of high performance and high costs are necessary, a circuit scale enlarges, or costs rise.
In the reproduction of the disc-shaped recording medium of the MCAV system using a plurality of heads, since different transfer rates are accessed, in order to optimize a reproduction signal obtained from each head, there is a case where an optimum one of a plurality of clock extracting circuits is selected and processes are executed. In this case, since an accessing time to access each clock extracting circuit and a switching time to switch the processes are necessary, there is such a problem that a processing time which is required until the reproducing operation reaches a stable region is long.
In the reproduction of the disc-shaped recording medium of the MCAV system using a plurality of heads, to enable the reproduction of the transfer rates in a wide range, there has been proposed a method whereby each transfer rate zone is divided into two zones of a high-transfer rate zone and a low-transfer rate zone and, upon extraction of the reproduction signal by each reproducing head, the signal processes are executed so that the sum of the transfer rates is always constant. In this case, there is such a problem that a control system for making management to set the sum of the transfer rates to be constant to each zone becomes complicated.
Those problems obstruct reduction of a signal processing time and an accessing time in a disc-shaped recording medium of the next-generation high-density recording which is predicted in future.
To solve the above problems, therefore, it is an object of the invention to provide reproducing apparatus and method which can realize rationalization of a scale of a clock extracting circuit of reproduction signals which are simultaneously obtained from a plurality of heads and realize low costs and a high processing speed.